Cells of the immune system protect the body against pathogens. If cells in our bodies are infected by viruses, or become cancerous, then killer cells of the immune system identify and destroy the affected cells. Cytotoxic T cells are very precise and efficient killers. They are able to destroy infected or cancerous cells, without destroying healthy cells surrounding them … By understanding how this works, we can develop ways to control killer cells. This will allow us to find ways to improve cancer therapies, and ameliorate autoimmune diseases caused when killer cells run amok and attack healthy cells in our bodies.